This investigation is undertaken to elucidate the association between the behavioral repertoire of the developing mammalian CNS and the maturation of brain neurotransmitter systems, concentrating upon those particular behavioral patterns exhibited by the developing rat pup during the first month of postnatal life and termed behavioral arousal. Abundant evidence suggests that such a pattern is influenced to a considerable degree by the maturation of central catecholaminergic (CA) mechanisms, and as a first approach, our studies will focus on the relationship between behavioral arousal and the maturation of dopaminergic (DA) and noradrenergic (NA) systems in brain. Delineation of the function of a particular DA pathway is accomplished by the intracerebral administration of 0.05 microns 1 (.1 microns g) - 0.1 microns 1 (0.2 microns g) volume of 6-hydroxydopamine (6-OHDA) into cell bodies of the nigroneostriatal (A9) or mesolimbic (A10) DA system. The accuracy, extent and specificity of the intracerebral 6-OHDA is assessed by 1) analysis of DA in striatum and nucleus accumbens-olfactory tubercle areas, the terminal fields of A9 and A10, respectively, utilizing either radioenzymatic assay or high performance liquid chromatography (HPLC), coupled with the Palkovits punch technique, 2) Falck-Hillarp histoflurorescence technique, 3) the standard morphometric mapping of the lesioned area. NA mechanisms in behavioral arousal are assessed after parenteral administration of 6-hydroxy-dopa and after lesioning ascending noradrenergic pathways with intracerebral administration of 6-OHDA. Behavioral parameters are correlated with endogenous concentrations of CA in specific brain areas (neostriatum, olfactory tubercle, nucleus accumbens, hypothalamus, hippocampus, pons-medulla). By exploring the relationship between the ontogeny of particular behavioral patterns and concurrent developmental alterations in specific CA pathways, we hope to better understand the fundamental neurochemical mechanisms underlying maturation of normal behavior. Such comprehension of the processes responsible for normal development may provide the nexus so basic to our unraveling the mechanisms responsible for those abnormal behavioral patterns characterizing a variety of neuropsychiatric disorders of childhood.